Patent documents 1 (JP 5-243036A) and 2 (JP 2004-153874A), for example, propose devices for reducing eddy-current loss generated in a coil in an electromagnetic device containing a plurality of coils.
In the document 1, a coil in a first layer and a coil in a second layer in which conductors are wound in opposite directions are electrically connected together to construct one coil unit, and this coil unit is wound on a field core that constructs a stator of a motor.
In the document 2, as opposed to the document 1, one of a plurality of coils positioned on the radially inner side of a stator is constructed by arranging a plurality of conductors whose width is smaller than the conductors constructing the other coil so that an eddy current generated in the coil due to a leakage flux is divided.
With the construction disclosed in the document 1, leakage fluxes from the field core and the like are separately linked to the individual coils. Therefore, eddy-current loss can be reduced in one coil unit. Since the amount of a linked leakage flux differs depending on the position of the coil, however, a relatively large eddy current is generated in the coil positioned in an area where a large amount of a leakage flux is linked. For instance, a leakage flux is linked more to the coil positioned on the radially inner side of the stator, and therefore a larger eddy current is generated in the coil positioned on the radially inner side than in the coil positioned on the radially outer side.
With the construction disclosed in the document 2, meanwhile, the conductor of the coil on the radially inner side where a larger amount of a leakage flux is linked is split into a plurality of pieces so that an eddy current is divided. Therefore, eddy-current loss can be reduced by the electrical resistance between the split conductors. However, the entire surfaces of the split conductors are insulatively coated by disposing an insulating member on the surfaces, and they are bonded together so as to obtain a desired width. Thus, the conductor that constructs the coil on the radially inner side is formed. Therefore, though the effect of reducing eddy-current loss is increased with increase in the number of split conductors, the proportion of insulating members is increased and a filling factor of conductors or an occupancy factor of space is lowered. That is, if an attempt is made to ensure a certain filling factor, the number of split conductors is limited, and the effect of reducing eddy-current loss may not be sufficiently obtained.